US20070253041A1 - Narrow angle hologram device and method of manufacturing same - Google Patents

Abstract

A method of manufacturing a master for producing a hologram device is provided. A first master is produced with a compensating angle. The second master is produced from the first master with an index matching material to reduce the interference pattern caused by internal reflections within the holographic plate of the master. The hologram device has a relatively narrow angle of reconstruction to provide visibility from a nearly perpendicular light source such as the headlight of an on-coming vehicle.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application claims benefit of the U.S. provisional patent application Ser. No. 60/505,945, filed Sep. 25, 2003, which is incorporated herein by reference.
TECHNICAL FIELD
• This invention relates to holograms, and particularly a narrow angle hologram device and method of manufacturing the same.
BACKGROUND OF THE INVENTION
• A hologram or hologram device is a device that includes a photosensitive film containing a recordation of a 3-dimensional image of a physical object. As is well-known, holograms generally become visible with an “angle of reconstruction”. An angle of reconstruction is a well-known term in the holographic art to mean an angle at which a light beam strikes the surface of the hologram during recording of the object image with respect to a perpendicular line to the hologram surface.
• Thus, when light from a light source strikes the hologram at the same angle of reconstruction the image was recorded at, the image becomes visible. In a conventional hologram, the angle of reconstruction AR is at least 45 degrees. As shown inFIG. 6B, the angle of reconstruction AR is 50 degrees. Basically, the light from alight source2 is well above the hologram and the viewer. In many applications, however, it may be advantageous to have a narrower angle of reconstruction. One such application, for example, may be a hologram road sign or house sign that illuminates when light from a vehicle strikes the hologram sign at near perpendicular angle to the hologram surface.
• Thus, it would be desirable to provide a hologram device having a narrow angle of reconstruction and a method of manufacturing the same.
SUMMARY OF THE DISCLOSURE
• According to the principles of the present invention, a hologram device having a narrow angle of reconstruction is provided. A photosensitive film is used to record a 3-dimensional holographic image of a physical object. The 3-dimensional holographic image has a narrow angle of reconstruction where the narrow angle is defined as a predefined angle that falls within a range of −30 degrees to +30 degrees, inclusive, relative to a perpendicular line to a surface of the photosensitive film. The 3-dimensional holographic image is recreated when a light illuminates the photosensitive film at the same narrow angle that was used to record the image.
• In one aspect of the invention, a method of making such a narrow angle hologram using an index matching technique is disclosed. Typically, an index matching material is interposed directly behind the hologram device during the recording process. This is designed to dissipate light and prevent it from causing interference with the recorded image.
• In another aspect of the invention, a method of making the narrow angle hologram using a predefined compensating angle is disclosed. In this case, an interim hologram device is used to initially record a 3-dimensional image. The image in the interim hologram device is transferred to a second hologram device, which is then used as a master to make multiple copies of the hologram. During the creation of the interim hologram device, the 3-dimensional image is recorded with an object beam at a preselected compensation angle relative to the perpendicular line to the surface of the interim hologram device. The predefined compensation angle is sufficiently low to substantially prevent the light used to reconstruct the 3-dimensional image from striking the second hologram device when the image is being transferred from the interim hologram device to the second hologram device. This feature also prevents noise from interfering with the image being recorded.
• In another aspect of the invention, both the index matching technique and the predefined compensation angle features are used to make a distortion free hologram device with a relatively narrow angle of reconstruction, preferably less than 30 degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates an object being prepared to be three dimensionally imaged.
• FIG. 2 illustrates the object ofFIG. 1 inserted into a mask attached to ground glass.
• FIG. 3 illustrates a setup for making a first master hologram with a recorded holographic image of the object ofFIG. 1 using a predefined compensating angle.
• FIG. 4 illustrates a setup for making a second master hologram from the first master hologram ofFIG. 3 using an index matching technique.
• FIG. 5A illustrates the light path of a collimated object beam for making the second master ofFIG. 4.
• FIG. 5B illustrates the light path of a collimated reference beam for making the second master hologram ofFIG. 4.
• FIG. 5C illustrates a method of making the second master hologram according to a conventional method and according to the present invention.
• FIG. 6A illustrates a hologram device made from the second master hologram ofFIG. 4 as seen by a viewer.
• FIG. 6B illustrates a conventional hologram device as seen by a viewer.
• FIGS. 7A and 7B show a plan view and a side view of a mounting bracket assembly for mounting a hologram device.
• FIG. 7C illustrates an alternate mounting bracket assembly for mounting the hologram device.
• FIG. 8A illustrates a method of aligning an apparatus using the hologram according to the present invention.
• FIG. 8B is a table of color/brightness of the reconstructed hologram image as a function of angular offset of the apparatus being aligned according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• The present hologram invention uses a relatively narrow angle of reconstruction of less than 45 degrees, preferably at most 30 degrees. In the hologram embodiment shown inFIG. 6A, for use as road or house signs for viewing by drivers, the angle of reconstruction is about 10 degrees so that when the vehicle headlights illuminate the hologram device20 (the number “7” in the example shown inFIG. 6A) at about 10 degrees to the perpendicular line from the hologram device, theimage6 reconstructed is at the maximum brightness which provides the widest viewing angle possible for the viewer.
• Generally, a master hologram plate or device is used to mass produce hologram copies. Preferably, two master holograms are created with a first master hologram H1 being created first and the second master hologram H2 being created using the first hologram H1. The two masters H1 and H2 are used to remove as much interference as possible.
• Hologram masters are typically made on a photosensitive glass plate exposed to laser light. In making the first master hologram H1, inventors have discovered that selecting a certain predefined compensating angle between an object to be recorded and the holographic plate H1 during the original recording substantially reduces reflections and crosstalk during the transfer process to create the second master hologram H2.
• In creating the second master hologram H2, inventors have also discovered that the laser beam incident to the holographic glass plate H2 at a relatively narrow reference beam angle relative to the perpendicular line to the hologram surface caused the light to reflect off the back face of the plate H2 and bounce between the faces of the glass, causing interference patterns such as several lines appearing throughout the hologram. According to the present invention, an optimized optical configuration was developed using an index matching technique to reduce the interference patterns caused by internal reflections within the holographic plate H2. In one embodiment, it can be achieved by applying a thin layer of index matching fluid between the second master hologram plate H2 and a very thick (e.g., ½ inch) glass plate or by suspending the holographic plate in a tank of the index matching fluid. Index matching is considered to be achieved when the system effectively acts as if the holographic plate is at least 4 times as thick, diffusing the light sufficiently so noise from back reflections is reduced by at least half. In the example of the thick glass plate, the thickness of the glass plate should be at least four times the thickness of the second master hologram H2. If an index matching fluid is used, then the depth of the fluid should be at least four times as much as the thickness of the second master hologram H2.
• A narrow angle hologram is a three dimensional image of object that appears to a viewer when exposed to light from the front at an angle of less than or equal to thirty degrees from the perpendicular plane of the object. The second master H2 required to produce thehologram device20 is created by a two step process. It is to be noted, however, that the steps in creating a first master H1 is preferred, but is an optional step.
• In the first step, a first master hologram H1 is made from an object to be three dimensionally imaged. In the second step, the image from the H1 is transferred to the final master (H2). Both H1 and H2 are created by exposing a holographic plate to optically manipulated laser light in a darkened room.
• Using a beam splitter, the laser is divided in two: a reference beam and an object beam. Each leg is redirected by mirrors and expanded with optics, preferably a spatial filter. The expanded beams are also collimated to stop their divergence and create a parallel wave front.
• The reference beam goes directly to a holographic plate. In the production of the H1 hologram, the other leg, the object beam, is directed to the object, reflecting off of it onto the holographic plate H1. During the transfer process, the object beam reconstructs the image recorded on H1 onto the final hologram H2. The two beams meeting at the holographic plate create a wave interference pattern that records the amplitude and phase of the light reflecting off the object. The reference beam and object beam have the same path length to the holographic plate but differ in power by up to 20-to-1 ratio, preferably a 3-to-1 ratio. Polarization of the laser light should be preserved. This can be accomplished by keeping the angle between the incident and reflected beams perpendicular at each mirror.
• Careful consideration needs to be made to avoid optical noise and physical vibration, which would distort or destroy the image. Possible vibration free configurations include using a pulse laser as the light source or affixing all components to a table isolated from structure-borne room noise. The former creates a high energy flash that freezes any microscopic movement. The latter can be created in an enclosed room with a vibration isolated optical table.
• The holographic plates are stored in light tight boxes until ready for exposure. After the exposures the plates are processed (typically using chemicals) to develop the recorded image and make them safe to be exposed to normal light levels. A detailed explanation of creating the first master H1, second master H2 and then thefinal hologram device20 will now be explained in detail with reference toFIGS. 1-7. Referring toFIGS. 1 and 2, a three-dimensional object22 (the number “7” in this example) of approximately 2 inches in height is formed from a transparent solid structure such as a transparent thermoplastic synthetic resin sold under the trade name of Plexiglas. Its front is coated with a clear dulling spray, creating a light diffusing finish, to avoid reflections of the laser light that would create optical noise. A blackopaque mask24 is made to outline theobject22. Theobject22 and themask24 are mounted onground glass26 as shown inFIG. 2 to form anobject module28.
• Referring toFIG. 3, the first master hologram H1 is created by recording the image ofobject22 onto a holographic plate H1 with a laser and processing the exposed plate. The master hologram H1, H2 includes a plate (generally a glass plate) coated with a high contrast, high resolution, photosensitive emulsion.
• A 1 Joule ruby pulse laser with a wavelength of 694 nm (not shown) was used to make the recording. The laser light goes through collimating optics (not shown) to make the light bundle parallel. Then the light goes through a beam splitter (not shown) which splits the collimated light into areference beam30 and anobject beam32. Thereference beam30 strikes the first master hologram H1 directly while theobject beam32 goes through the object module at a perpendicular angle to theobject22 and then strikes the first master hologram at a predefined compensation angle CA which is measured relative to a perpendicular line to the H1 surface. The compensation angle could be from 0 to 45 degrees.
• The mountedobject22 is angled with respect to the perpendicular line of the first master hologram plate H1. This is done to prevent reflections and crosstalk of the laser light used to reconstruct the image recorded on H1 from hitting the H2 master during the transfer process. This compensating angle of 0 to 45 degrees is determined by the relative size of the first master hologram H1 and the second master hologram H2, and the distance between them during the transfer process. In the example shown, a 20 degree angle with respect to the perpendicular line of the holographic plate H1 was used for a 11.8″×7.9″ H1 spaced 12″ from a 5″×4″ H2.
• Once the exposed first master hologram H1 is processed, it becomes a laser viewable transmission hologram. The recorded image is reconstructed (becomes visible) when exposed to laser light from the rear at the same angle as the reference beam was set during the original recording.
• Referring toFIG. 4, the image recorded on the first master hologram H1 is reconstructed and transferred to the second master hologram H2 using a novel index matching technique, e.g., with an index matched material (seeFIG. 5C) which has a similar index of refraction as that of the second master H2. The transfer of image from H1 to H2 effectively makes a hologram of the original hologram. The index matched materials that may be used in the present invention include glycerol, glass, mineral spirits, xylene, trichloroethylene or the like which have similar index of refraction as H2. Index matching is used when the reconstruction angle AR is 0 to 30 degrees, preferably 5 to 15 degrees for the hologram device created. 10 degrees was actually used in the embodiment shown.
• For this second step, a 400 mW continuous wave green laser with a wavelength of 532 nm (not shown) was used. The image was slightly reduced in size from the original recorded object due to account for the difference in laser wavelengths when creating the two masters H1 and H2. The size would be matched if the same wavelengths were used in both steps.
• The laser light goes through aspatial filter34, collimatingoptics36 andmask38, which then strikes the rear surface of the first master hologram H1 at the same angle as thereference beam30 relative to the H1 plate surface which was used in the first step of creating the first master hologram. That causes afocused image40 of theobject22 recorded in the first master hologram H1 to be reconstructed.
• At the same time, the same laser light goes through thespatial filter34, collimatingoptics36 andmask38, and then strikes the surface of the second master hologram H2 at an angle of reconstruction AR which is measured relative to the perpendicular line to the second master hologram H2 surface. As shown, the angle of reconstruction AR used inFIG. 4 is 10 degrees. Theimage40 reconstructed by the first master hologram H1 is then recorded in the second master hologram H2. Afterwards, the exposed second master hologram H2 is processed in a conventional manner.
• InFIG. 4, theindex matching material42 which is positioned behind the rear surface of the second master hologram H2 as will be explained in more detail with reference toFIG. 5C.
• As discussed above, the first step of creating the first master hologram H1 as shown inFIG. 3 is an optional step. If that step is omitted, then instead of the H1 master reconstructing theimage40, the physical object22 (or the object module28) would be positioned in the place where theimage40 would have been.
• FIG. 5A shows that the compensating angle CA that was used to create the first master H1 is reversed. In other words, inFIG. 3, the object was tilted back by 20 degrees while inFIG. 4, the reconstructed image stands straight and the first master hologram H1 is tilted back by 20 degrees (CA). As can be seen, the compensation angle CA is carefully chosen to be sufficiently low such that the collimated object beam for the first master hologram H1 does not strike the second master hologram H2, which is sufficient to prevent crosstalk distortion that would occur if the beam used to reconstruct the image recorded on H1 were to strike the H2 plate.
• FIG. 5B shows that the compensating angle CA also prevents the collimated reference beam for creating H2 from reflecting off of H1 back onto the H2 plate.
• Referring toFIG. 5C, the right most figure illustrates a conventional hologram device where the angle of reconstruction (reference beam angle with respect to the perpendicular line from a glass mount44) is relatively wide at 55 degrees. In that case, even though there are some internal reflections within theglass mount44 and holographic plate, they may not cause serious problems.
• Referring to the middle figure inFIG. 5C, without index matching, the collimatedreference beam50 for the second master hologram H2 incident to aglass plate46 is at a narrow angle (in thiscase 10 degrees) and the beam reflects off the back of the second master hologram plate H2 and bounces between the faces of theglass plate46, causing fringe distortions (interference patterns consisting of several lines throughout the hologram).
• In the left most figure and according to the present invention, the second master H2 is laid in a thin pool of a clearindex matching fluid52, such as mineral spirits, on top of a thick (more than ½ inch)glass plate48 to reduce internal light reflections within the holographic plate. The thin layer offluid52 fills any small gaps that may exist between theglass plate48 and H2. Alternately, the second master holographic plate H2 can be suspended in a tank filled with theindex matching fluid52 only. In the embodiment shown, the index of refraction for thethick glass plate48, the fluid52 and H2 are approximately 1.5. This “index matching” technique diffuses and dissipates the light50 after it initially passes through the second master holographic plate H2, reducing the interference patterns caused by back reflections.
• Using the index matching technique, the image recorded in the first master hologram H1 is transferred to the second master hologram H2. The H2 is processed to permanently fix the recorded image on the plate in a conventional manner. The second master hologram H2 is then used to make hologram copies20.
• One application of the above technique for manufacturing a master is in a hologram device containing a series of holograms such as number signs, with a narrow angle of reconstruction, that are combined to create an individual street address that projects out from the sign and illuminates (with no power required) from simply an oncoming vehicle's headlights, so that visitors or emergency vehicles can identify an address at night. Theholograms20 are recorded on transparent photosensitive film and applied over matching printeddigits54 as shown inFIG. 6A.
• When light from an appropriate angle is not shining on the holograms, they are transparent and the printed number underneath is visible, so the address can be seen at all times. The mounting hardware installs on a mailbox, post, pole or tree and is vertically and horizontally adjustable for achieving the optimal angle to traffic for maximum brightness and clarity.
• Referring toFIG. 6A, the image recorded on thehologram device20 is reconstructed as reproducedimage6 when the hologram device is exposed to white light coming from the front at the same angle as the reference beam angle used during its recording.
• To make thehologram device20, copies of the narrow angle master hologram H2 are made on transparent photosensitive film backed with a clear adhesive. They are adhered over asticker54 printed with flat (2D) images that match the holographic images recorded on the photosensitive film. The sticker is most effective if it is light colored with the image printed in dark ink. The ink of the printed number acts as the dark background behind the matching hologram, which maximizes the brightness and contrast when the hologram is exposed to an appropriate light source. Theholograms20 illuminate when exposed to light from the front at a narrow angle of reconstruction of preferably less than 30 degrees from the perpendicular line of thehologram device20. When such a light source is not present, theholograms20 are transparent and theflat image54 printed on the stickers underneath are visible.
• Another application of the present invention is in alignment of one structure to another. Theholograms20 shift in color and brightness depending on the angle at which the light strikes the hologram surface. As shown in the table ofFIG. 8B, the reconstructed image becomes a very bright orange color at a predetermined resonant angle.
• The color at the angle of reconstruction (zero offset) and the rate of color change against the angular displacement can be changed to suit different applications as appropriate. The color at the angle of reconstruction can be set by a) choice of laser wavelength together with film/plate wavelength sensitivity, b) fine tuning of the optical geometry during transfer, or c) chemical and/or thermal conditioning of the film/plate, or d) a combination of the above. This color becomes the center of the light spectrum around the resonance (reconstruction) angle. For instance, if green is the chosen as the “center” color, then deviation in one direction turns the color progressively to blue then violet. In the other direction, the color turns to yellow to orange to red.
• The rate of change (angular displacement vs. color) can be controlled by broadening or limiting the viewing angle of the hologram. Broadening would yield more precision, providing less color shift per degree of angular displacement. Limiting would have the converse effect. The viewing angle can be manipulated, for example, by changing the ratio in sizes between the H1 and H2 during the transfer process. For instance, a very large H1 transferred to a small H2 broadens the viewing angle. Using lasers with different wavelengths in the creation of H1 vs. H2 also can contribute to the viewing angle.
• InFIG. 8B, the predetermined angle is zero degrees relative to the perpendicular line to thehologram20 surface with the center color being orange. This property can be used for angular positioning or alignment, such as a left-right-center-up-down alignment indication when truck or fork lift drivers approach a dock or shelf, or when a rocket docks to a space station since a minor shift in the angle creates a highly visible shift in color and brightness, or optical fiber alignment, providing greater precision than was possible previously.FIG. 8A shows thehologram20 being used to align asubmarine56 approaching a docking station (not shown) having thehologram20 as an attachment. The light58 coming from thesubmarine56 strikes thehologram20. The top submarine is coming in slightly off axis from the perpendicular line to thehologram surface20 as the color is yellow and is not very bright. On the other hand, the bottom submarine is coming in directly on the axis. As a result, the color of the image in thehologram20 is orange and is very bright.
• Referring to FIGS.7A-C, thephotosensitive film holograms20 mated with thestickers54 are applied to a mountingbracket70. The bracket includes a mountingplate60, up/downswivel member62 attached to the mounting plate, left/right swivel member63 rotatably coupled to the up/downswivel member62 by ascrew65, left/right swivel member and numbers plate64 on which thehologram20 is mounted or affixed. The left/right swivel member63 is rotatably coupled to the up/downswivel member62 by thescrew65 and attached to thenumbers plate64 by ascrew66. Thebracket70 is adjustable for achieving the optimal viewing angle.FIG. 7C shows an alternative adjustment mechanism where ascrew72 is tightened with a nut in two slotted C-shaped orcurved arms74.
• The foregoing specific embodiments represent just some of the ways of practicing the present invention. Many other embodiments are possible within the spirit of the invention. Accordingly, the scope of the invention is not limited to the foregoing specification, but instead is given by the appended claims along with their full range of equivalents.

Claims (14)

1-5. (canceled)

6. A method of making a narrow angle hologram comprising:

(a) using an index matching technique, recording a 3-dimensional holographic image of an object on a hologram device at a narrow angle defined as an angle within a range of −30 degrees to +30 degrees, inclusive, relative to a perpendicular line from a surface of the hologram device; and

(b) developing the image recorded in the hologram device.

7. The method according toclaim 6, prior to step (a), further comprising:

(c) recording the 3-dimensional holographic image of the object on an interim hologram device with an object beam at a predefined compensation angle relative to a perpendicular line from the surface of the interim hologram device, the predefined compensation angle being sufficiently low to substantially prevent the light used to reconstruct the 3-dimensional holographic from striking the hologram device during step (a).

8. The method according toclaim 6, wherein step (a) includes recording the 3-dimensional holographic image with an index-matching material positioned behind the hologram device, the index-matching material being index-matched with the second hologram device.

9. The method according toclaim 8, wherein the index-matching material comprises:

a solid transparent index-matching material; and

a thin layer of index-matching fluid interposed between the hologram device and the solid transparent index-matching material.

10. The method according toclaim 8, wherein the depth of the index matching material is at least four times as high as the depth of the hologram device.

11. A method of making a hologram comprising:

recording a first 3-dimensional holographic image of an object on a first hologram device;

using an index matching technique, recording on a second hologram device a second 3-dimensional holographic image based on the first 3-dimensional holographic image recorded in the first hologram device at a narrow angle defined as an angle within a range of −30 degrees to +30 degrees, inclusive, relative to a perpendicular line from a surface of the second hologram device.

12. The method according toclaim 11, wherein the step of recording a second 3-dimensional holographic image on the second hologram device includes recording the second 3-dimensional holographic image with an index-matching material positioned behind the second hologram device, the index-matching material being index-matched with the second hologram device.

13. The method according toclaim 12, wherein the index-matching material comprises:

a solid transparent index-matching material; and

a thin layer of index-matching fluid interposed between the second hologram device and the solid transparent index-matching material.

14. The method according toclaim 13, wherein the depth of the solid index matching material is at least four times as high as the depth of the second hologram device.

15. The method according toclaim 12, wherein:

the index matching material includes an index-matching fluid; and

the depth of the index matching fluid is at least four times as high as the depth of the second hologram device.

16. The method according toclaim 11, wherein the step of recording a first 3-dimensional holographic image includes recording the first 3-dimensional holographic image with an object beam at a predefined compensation angle relative to a perpendicular line the surface of the first hologram device, the predefined compensation angle being sufficiently low to substantially prevent the light used to reconstruct the first 3-dimensional holographic from striking the second hologram device during the step of recording a second 3-dimensional holographic on the second hologram device.

17. The method according toclaim 11, further comprising generating a plurality of duplicate hologram devices using the second hologram device as a master.

18. A method of making a hologram comprising:

recording a first 3-dimensional holographic image of an object on a first hologram device with an object beam at a predefined compensation angle relative to a perpendicular line from a surface of the first hologram device; and

using an index matching technique, recording on a second hologram device a second 3-dimensional holographic image based on the first 3-dimensional holographic image recorded in the first hologram device at a narrow angle defined as an angle within a range of −30 degrees to +30 degrees, inclusive, relative to a perpendicular line from a surface of the second hologram device so as to cause light dissipation after the light goes through the second hologram device;

wherein the predefined compensation angle is sufficiently low to substantially prevent the light used to reconstruct the first 3-dimensional holographic from hitting the second hologram device during the step of recording a second 3-dimensional holographic image on the second hologram device.

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